“Mars is giving us observations both like and unlike Earth, and that’s very exciting,” says Joseph Grebowsky at the NASA Goddard Space Flight Center in Greenbelt, Maryland, head of the team that found these Martian metals.

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The space between planets is full of metallic dust and rocks. As they are drawn into a planet’s atmosphere, they burn up, leaving behind metal particles like iron and magnesium. On Earth, the behaviour of those particles is mostly controlled by the planet’s strong magnetic field. They use magnetic fields as a sort of highway, and stream along the magnetic field lines to form thin layers throughout the atmosphere.

But Mars has no such field. The planet does have small regions with weak magnetic fields in its southern hemisphere, but without a global field like Earth’s, it should not be able to form the layers that MAVEN sees.

“Something is causing these layers – something is pushing them around – but we don’t know what,” says Grebowsky. Mars’s nubs of magnetic field certainly play a part, and winds through the atmosphere probably do as well, but the exact mechanism must be different from the one at work on Earth.

Grebowsky says that he has expected that the Martian atmosphere would have metal ions for years, but this is the first time that a spacecraft there has confirmed their continuous presence.

Heavy metal

He and his colleagues also found an unexpected distribution of iron and magnesium ions at Mars. Iron is heavier than magnesium, so it should sink and leave less iron than magnesium higher in the atmosphere. Instead, the two are well-blended much higher in the atmosphere than expected.

“The profiles are surprisingly ordered with respect to altitude,” says Grebowsky. “It’s very unlike at Earth.”

These wavy clouds of metals could be related to chemistry and climate in Mars’s upper atmosphere. They may even help explain how the planet lost much of its atmosphere to space, leaving it dry and barren.

“In terms of understanding the habitability of a planet, it’s very important to be sure about understanding atmospheric processes,” says Guillaume Gronoff at NASA’s Langley Research Center. “Here it’s showing that there are a couple of things that we don’t get.”

These new MAVEN findings yield more questions than answers: how do the metal ions get so high up in the atmosphere? How do they form layers like Earth’s without a strong magnetic field? Why are they mixed in so well together?

The models that we have now of Mars’s atmosphere can’t explain any of these phenomena. “This is neat because it shows us that the Martian atmosphere is an atmosphere all by itself,” says Dean Pesnell, who is also based at the NASA Goddard Space Flight Center but was not involved in this work. “It’s not just another Earth that’s a little different.”